FIG. 6 shows an example of an outline constitution of a laser oscillating apparatus of a background art. The laser oscillating apparatus of the background art will be explained in reference to FIG. 6.
The laser oscillating apparatus of the background art includes electrodes 2, 3 at a periphery of discharge tube 1 constituted by a dielectric member of glass or the like. Electrodes 2, 3 are respectively connected with power sources 4. Discharge space 5 is formed at inside of discharge tube 1 interposed by electrodes 2, 3. Further, a total reflection mirror and partial reflection mirror 7 are provided. Laser beam 58 is outputted from partial reflection mirror 7. Arrow mark 9 designates a direction in which laser gas flows. Further, heat exchangers 11, 12 for lowering a temperature of the laser gas, a temperature of which rises by discharge in discharge space 5 and by operation of a centrifugal blower, are provided. Laser gas is circulated by using blowing means 43. As blowing means 43, for example, a centrifugal blower, mentioned later, or the like is used. Laser gas flow path 10 and discharge tube 1 are connected by laser gas introducing portion 14.
FIG. 7 shows an example of an outline constitution of a laser working machine in the background art. The laser working machine of the background art will be explained in reference to FIG. 7.
Laser beam 58 outputted from the laser oscillating apparatus shown in FIG. 6 is reflected by reflecting mirror 15 and is guided to a vicinity of work 16. Laser beam 58 is converged into a high density energy beam by condenser lens 18 provided at inside of torch 17 and irradiated to work 16 to process the work 16. Work 16 is fixed on work table 19 and a predetermined shape is obtained by moving torch 17 relative to work 16 by X axis motor 20 or Y axis motor 21.
FIG. 8 shows a structure of a periphery of a centrifugal blower in the laser oscillating apparatus.
Motor 22 in centrifugal blower 43 includes motor rotor 22a in a direction orthogonal to a gravitational force direction (arrow mark G direction), and includes motor stator 22b on a lower side in the gravitational force direction (arrow mark G) (that is, lower side of drawing). A front end of shaft 29 coupled with rotor 22a is provided with blade wheel 23 and diffuser 24. Laser gas is sucked from suction port 25 from an upper direction in the gravitational force direction and is provided with kinetic energy by a centrifugal force by rotation of blade wheel 23. Thereafter, the kinetic energy is converted into pressure by diffuser 24 and a gas having pressure about 1.5 times as much as that of the suction port 25 is delivered from delivery port 26.
Oil 27 is contained at a portion of casing 31 containing motor 22 below centrifugal blower 43 and is used for lubricating bearing 28 and cooling rotor 22a. When oil mist generated from oil 27 invades laser gas circulated by blade wheel 23, a purity of laser gas is reduced to bring about a significant drawback in laser oscillation. Hence, in order to restrain oil mist from invading a laser gas circulating portion (that is, laser gas flow path 10), partition wall portion 50 is provided to separate motor chamber 54 and gas circulating chamber 35. A clearance (clearance 57 as shown by FIG. 9) of several 100 μm is provided between partition wall portion 50 and shaft 29 to thereby construct a constitution of not hampering rotation of the shaft.
As described above, the clearance of several 100 μm is present at partition wall portion 50 and therefore, oil mist invades gas circulating chamber 35 from motor chamber 54 by passing the clearance by vacuum diffusion. In order to prevent this, by always exhausting a constant amount of gas from motor chamber 54 by using vacuum pump 32, a pressure of motor chamber 54 is constituted by a pressure lower than that of gas circulating chamber 35. A path reaching vacuum pump 32 from motor chamber 54 is provided with electromagnetic valve 33, which is opened and closed as needed.
FIG. 9 shows a detailed structure of partition wall portion 50. Clearance 57 of several 100 μm is provided between shaft 29 and metal seal 36 and a constant amount of laser gas always flows to clearance 57. By the always flowing laser gas, invasion of oil mist from motor chamber 54 to gas circulating chamber 35 can be prevented.
Laser gas flowing through clearance 57 between shaft 29 and metal seal 36 is exhausted to outside as it is by vacuum pump 32 and therefore, it is necessary to supply an exhausted amount of laser gas to gas circulating chamber 35 by other route. This constitutes a consumption amount per unit time of laser gas in the laser oscillating apparatus and the laser working machine to share a large weight in running cost.
Therefore, it is a serious problem in view of reducing running cost how to reduce the consumption amount of laser gas per unit time. It is necessary to narrow clearance 57 in order to reduce the laser gas consumption amount. However, generally, laser gas passing through the clearance 57 includes sputtering particles by laser gas discharge and small unavoidable particles which are generated in a component assembling step. When clearance 57 is narrowed to about several 10 μm, there is a possibility of deteriorating reliability by clogging clearance 57 with the particles.
In the case of the background art of JP-A-10-184593, it is only disclosed to simply specify a shape and a dimension of metal seal 36 with regard to clearance 57 and it is not pointed out to prevent clogging of foreign matters as a problem.
Further, although JP-A-2004-207467 discloses an example of using a PTFE material at a partition wall portion and forming a minimum clearance by wearing PTFE by forcibly bringing the PTFE material and a rotating shaft into contact with each other, a high accuracy is difficult to ensure by the method.